Voltage divider



Patented ill/liar. 9, 1943 VOLTAGE DIVIDER Victor John Terry and Thomas Frederick Stanley Hargreaves, London, England, assignors to International Standard Electric Corporation, New

York, N. Y.

Application April 9, 1942 Serial No. 438,300 In Great Britain March 7, 1941 8 Claims. (CL 171-312) This invention relates to the balancing of the loads on an electric supply, and is particularly useful in a telegraph system with double-current working, for the purpose of maintaining an equipotential division of the supply as between positive and negative signals.

An object of the invention is to provide an electronic potential divider capable of maintaining an equal division of potentials between approximately 140 and 200 volts with unbalanced loads varying from to 120m. or more. Unlimited balanced loads may be added in addition to the unbalanced loads.

The invention consists in an arrangement for connected respectively between the positive terminal T3 and the centre point T4, and between the centre point T4 and the negative terminal T5.

Thus, if the desired equipotent-ial division of the supply as between the two loads Li and L2 is attained, each load will be fed at 80 volts.

Now with the positive and negative loads equal to one another, the centre-point T4 would be at a potential equidistant from the positive and negative potentials of the respective terminals T3 and T5-when RI and R2 were equal to one another. But if the load on say the positive side Ll were to increase in relation to that on dividing a direct-current supply into halves of the negative side, so that the resistance on the equal voltage and for maintaining the equality positive sidev were decreased, the potential of of said division independently of varying inthe centre-point T4 would be displaced in the equalities in the loads on the two halves, in which positive direction. This could be compensated at least one of two voltage-dividing resistors confor, by decreasing the resistance of the potentinected in series across the supply is such that ometer element R2 on the negative side by an its resistance decreases and increases as the voltamount sufficient to restore the equality beage across it increases and decreases; tween the resistance Tl-CP and the resistance In a double-current telegraph system, it is CP-T2, this amount depending upon the origdesirable that the potentials of both positive and inal relationship between the quantities Ri, R2, negative signals should be the same. Where a LI, L2, and to that extent varying in a complex common battery is supplying a plurality oi sendmanner. ers, this desired equality may be lacking owing The present invention makes use of thermionic to the fact that the two loads, positive and negatubes as the potentiometer resistances RI and tive, may be diilerent, these loads each being the R2, arranging these valves so that their anode sum of the instantaneous loads due to the incharacteristic resistances shall vary in the direcdividual senders, and therefore each varying from tion, and at leastapproximately to the extent, instant to instant as signalling progresses. that is necessary to compensate for changes in The invention will be better understood from the loads; and Fig. 2 shows an electronic centrea reading of the following description in contap stabiliser embodying the invention. junction with the accompanying drawing in The potential dividing resistances RI and R2 which are the combined anode impedances of two tri- Fig. l is a schematic diagram used in the exodes V3 and V4 (or two banks of triodes) conplanation oi the invention, and nected in series and controlled by two high mag- Fig. 2 shows one embodiment of the invennification pentodes V2 and V1 respe y In tion. the following description triode" refers to either Fig. l is a rudimentary diagram showing how one triode or a bank of triodes in parallel. the common power supply of a double-current The anode current of one triode is added to telegraph system feeds the individual senders the more light y loaded Side Of the Potential over a potential divider. The direct current vider, in order to make the load on that side sources, of say 160 volts, is connected to the qual'to the larger unbalancing load. The anode positive and negative input terminals TI and circuit of the other triode is connected across T2 of the potential divider PD, consisting of a the heavily loaded side in order to deal with any potentiometer t l t 31 and 2, o probable unbalance in the reverse direction, and th utput d t potential id P has a it is normally cut-off. When the external loads positive terminal T3, a centre tap T4, and a are balanced, both triodes o t s t y; but negative ter inal T5 in the worst case, the total drain of the whole Thespositive and negative loads LI and L2, circuit does not exceed 10 ma. for a circuit suiteach consisting of the individual telegraph sendable for unbalance currents up to 120 ma. ers that at the instant under consideration are With one high magnification pentode, the sending either positive or negative signals, are phase of operation is such that it operates di rectly on to one of the triodes. The other triode requires a phase inversion, so that the second pentode is used to perform this function.

Under normal balanced conditions, the potential dividing triodes are almost cut oil, but the two pentodes are biased for eflicient amplification. If the positive side of the circuit is more heavily loaded than the negative side (i. e., Ll is greater than L2, so that the resistance of LI is less than that of L2), then the centre point T4, and hence the cathode of the first pentode,

VI, tends to approach the potential of the positive side T3. This is equivalent to putting the grid of VI more negative, so that the valve Vl will tend to be cut off. The anode potential of VI will thus be raised, so that the grid potential of the triode (V4) on the negative side will be made more positive and this triode will conduct more freely.

At the same time, the grid of the phase reversing pentode (V2) becomes more positive and this valve will take more anode current. This reduces its anode potential and in turn reduces the grid potential of the triode (V3) in the positive side, due to the increased voltage drop through the resistances A and B which will cutoil the triode in the positive side still further. The combination of these two conditions is that the triode in the positive side is cut off, and the triode in the negative side is conducting, to form a load on that side, which tends to bring the centre tap towards the negative side and hence stabilise the circuit.

Conversely, if the negative side of the circuit is more heavily loaded than the positive side; then the centre point, and hence the cathode of the first pentode V1, tends to approach the negative side. This is equivalent to putting the grid of V1 more positive, so that V1 will take more anode current and its anode potential will fall. This makes the grid of the triode (V4) on the negative side more negative so that it is cut off. At the same time the grid of the phase reversing pentode V2 is made more negative and the plate current of the valve V2 will be reduced. As less anode current passes through the anode resistance A of this pentode, the anode potential becomes more positive with respect to the centre point of the circuit. The phase reversing pentode has a subsidiary anode resistance B connected to the positive side of the supply, whose function is to make the grid of the triode V3 positive with respect to its cathode and hence give it a wider range of control. As the grid of the triode V: on the positive side is connected directly to the anode of the phase reversing pentode V2 its potential becomes more positive and the triode conducts more freely. Thus the triode in the positive side is conducting, forming a load on that side, and the triode in the negative side is cut oil; so that the centre tap tends to move towards the positive side and hence stabilise the circuit.

With a balanced load on a 160 volt supply: the grid of the first pentode V1 is at about -3 volts, which gives an anode current of about 0.8 ma. and an anode voltage of about 30 volts. These conditions require a 120 volt battery HT with the grid of the phase reversing pentode tapped at about 15 volt. This makes the grid of the triode (V4) in the negative side about 10 volts so that it takes about 2 ma. anode current (for each valve in the parallel circuit). The grid of the phase reversing pentode is about minai but the tube takes about 0.25 ma, because the cathode is about +10 volts from this same point (i. e., the grid is about -5 volts with respect to the cathode). The voltage drop through the anode resistance A is about volts, so that the anode of the phase reversing pentode and hence the grid of the triode (V3) in the posi- Initial adjustments Initial adjustments are made to the potentiometers P1 and P2 and the grid battery tapping by observations of the plate currents, viz:

+5 volts with respect to the negative supply ter- V1=0.8 ma.; V2=0.25 ma., Va=2 ma. per tube (i. e., 6 ma. for 3 tubes in parallel). V4=2 ma. per tube.

(The anode current of V4 will be slightly higher than that of V: because the surplus anode current of V1, which does not pass through V2, passes through V4.) v

The initial adjustments are made in order to approach the above conditions as nearly as possible, and they should be made with no unbalanced load on the circuit (the centre tap from the loads should preferably be disconnected) and the supply should be approximately at its mean voltage or with a tendency towards its lower value.

A 35-0-35 ma. meter is used in conjunction with a selector switch to measure the anode currents of all tubes in the circuit. This meter is also used to measure the unbalance voltage, by measuring the unbalance current between the centre point of the circuit and a virtual centre point formed by two equal resistances (not shown) across the supply.

The circuit need not necessarily have the same number of tubes for V: as there are for V4. If a greater degree of unbalance is experienced on one side, then the heavier loaded side may have fewer tubes than the lighter loaded side, the number of tubes depending on the degree of unbalance likely to be experienced.

The speed of operation of the tube circuit is very high but it is supplemented by large condensers Cl, C2, C3 in order to accommodate large transient currents.

It will have become evident from what has gone before, that the triodes V3 and V4 may be considered either as the potential dividing resistances RI and R2 or as parts of the loads LI and L2. These two ways of regarding the circuit are quite consistent with one another, since, in Fig. l, the resistance RI or R2 is identical in respect of its electrical connections with any one if: the components of the respective load Ll or What is claimed is:

1. An arrangement for dividing a direct-current supply into halves of equal voltage and for maintaining the equality of said division independently of varying inequalities in the loads on the two halves, comprising; a potentiometer across the supply; an amplifying pentode having its control grid connected directly to an adjustable centre-tap on the potentiometer, its anode connected over a resistance to the positive having its control grid connected directly to the anode of the phase-reversing pentode, its anode connected over a resistance to the positive supply line, and its cathode connected directly to the centre point; and a bank of one or more triodes I having its control grid connected directly to the negative end or the high-tension supply to the amplifying pentode, its anode connected over a resistance to the centre point, and its cathode connected directly to the negative supply line.

' anode, a cathode and a control grid, means for connecting one of said loads across one of said resistances and the other of said loads across the other of said resistances, and means for rendering said control grid more or less positive as the load across said thermionic tube decreases or increases respectively in relation to the load across the other resistance.

3. An arrangement for dividing a direct current supply into halves of equal voltage and for maintaining the equality of said division independently of varying inequalities in the loads on the two halves, comprising two voltage dividing resistances connected in series across the supply, each including the anode impedance of a thermionic tube, means for connecting one of said loads across one of said thermionic tubes and the other of said loads across the other of said thermionic tubes, and means for varying the anode impedances of said tubes so that said impedances'increase and decrease with increase and decrease of the loads connected across them.

4. An arrangement for dividing a direct current supply into halves of equal voltage and for maintaining the equality of said division independently of varying inequalities in the loads on the two halves, comprising two voltage dividing 5. An arrangement according to claim 4 in which said last-mentioned means comprises a second thermionic tube comprising a cathode, an anode and a control grid, and further comprising a potentiometer connected across said supply, a connection from said anode of said second tube to the positive side of said supply, a connection from said cathode of said second tubeto said junction point, a connection from said grid of said second tube to a center tap on said potentiometer, and a furthenconnection from the anode of said second tube to the control grid of the other tube.

6. An arrangement for dividing a direct current supply into halves of equal voltage and for maintaining the equality of said division independently of varying inequalities in the loads on the two halves, comprising two voltage dividing resistances connected in series across the supply, at least one of said resistances comprising the anode resistance of a thermionic tube having a cathode, an anode and a control grid, means for connecting one 01' said loads across one or said resistances and the other of said loads across the other of said resistances, a connection from the positive side of said supply to said anode, a connection from the Junction point of said resistances to said cathode, and means or causing resistances connected in series across the supply, at least one of said resistances comprising the anode resistance of a thermionic tube having a cathode, an anode and a control grid, a conthe potential of said control grid to follow the variations in potential of said junction point due to inequalities in said loads.

'7. An arrangement for dividing a direct current supply into halves of equal voltage and for maintaining the equality 01' said division independently of varying inequalities in the loads on the two halves comprising a potentiometer connected across the supply, an amplifying thermionic tube having a control grid connected to an adjustable center tap on said potentiometer, its anode connected to the positive side or the supply, and its cathode connected to the center point between the two loads, a phase-reversing amplifying thermionic tube having a control grid connected to an adjustable point in the high tension supply to said amplifying thermionic tube, its anode connected to said center point, and its cathode connected to the negativeside of the supply, a further thermionic tube having a control grid connected to the anode of said phase-reversing tube, its anode connected to the positive side of the supply and its cathode connected to said center point, and a still further thermionic tube having a control grid connected to the negative side of the high tension supply to said first mentioned amplifying tube, its anode connected to said center point, and its cathode connected to the negative side or the supply.

sistances to said anode, and means for causing 8. An arrangement according to claim 7, wherein a condenser is connected across each load.

VICTOR JOHN TERRY. THOMAS FREDERICK STANLEY HARGREAVES. 

